Mobile phones typically use whip or helix antennas, which have hemispherical coverage patterns. With a hemispherical pattern, the mobile phone may be oriented anywhere in azimuth with respect to the cell site without affecting reception, assuming no blocking objects are present.
One disadvantage of conventional mobile phones is that the antenna radiates electromagnetic energy into a user's head equally compared to other angles. Antenna design must be carefully managed in order to comply with Specific Absorption Rate (SAR) specifications, which limit the amount of electromagnetic energy a user's head may receive.
Another disadvantage is that gain in the direction of a user's head is diminished because of blockage by the head. The energy directed into the head makes it difficult to meet SAR requirements, and is to some degree wasted because it is blocked by the head. Conventional designs employ an external whip antenna and/or an external helical antenna that each has hemispherical coverage. Some mobile phones use internal antennas such as the Inverted-F type or microstrip designs such as a patch or parasitic patch, which have hemispherical patterns or a dipole-like pattern as illustrated in FIG. 1. FIG. 1 also illustrates an external helical antenna.
FIG. 1 is a diagram illustrating a front view of a conventional mobile phone 10 with an electromagnetic pattern 12 from a center-fed dipole 14 located inside the mobile phone 10. The dipole 14 has a length of approximately L/2, where L is the length of one electromagnetic wave at the frequency at which the dipole 14 operates.
FIG. 2 is a diagram illustrating a side view of the conventional mobile phone 10 with the electromagnetic pattern 12 from the dipole 14. Electromagnetic pattern 12 has a null, but in order to align that null with a user's head during operation the dipole 14 would have to be rotated 90 degrees. At the frequencies typically used with mobile phones, a mobile phone housing such a rotated dipole would be very thick.
Accordingly, what is needed is a mobile phone having a directed beam antenna that assists in meeting SAR specifications, reduces wasted energy towards a user's head, and increases energy in other directions. The present invention addresses such a need.